Portable personal computing devices such as smart phones, Personal Digital Assistants (PDA), portable computers, tablet computers and audio devices such as digital music players have become ubiquitous in recent years. These devices usually have different built-in physical electrical interfaces such as USB, FireWire, RS232 serial port and audio plug, among others. In almost all of these devices, and in particular in the audio devices, the audio plug is a common interface. The audio plug of a device acts as a receptacle for an audio jack connector which is used for transmitting analog signals including audio signals. The audio plug may also be used to connect to headphones, speakers, microphones, and hands-free devices, among others.
Previously, many mobile phones used to have their own proprietary form of audio plugs configured to be used with cables outfitted with matching proprietary audio jacks. However, recently the functionality of mobile phones has changed so much that most mobile phones are now also digital music players, payment devices, navigation devices and cameras, among others. Additional accessory devices including headphones, printers, and card readers, among others, may be connected to the mobile phones in order to listen to music, print and complete payments, among others. Therefore, due to these added functionalities and the need to connect additional accessory devices to mobile phones, 2.5 mm audio plugs and/or 3.5 mm audio plugs can now be found on most middle to high-end mobile phones. In order for an accessory device to connect and communicate properly with a mobile phone via an audio jack, a common ground between the accessory device and the mobile phone must be established. Otherwise, signals transmitted from the accessory device cannot be interpreted properly by the mobile phone.
Most 4-pole audio plugs include four contact points that are connected to the Left-channel of stereo sound output (L-CH), Right-channel of stereo output (R-CH), Microphone input (MIC-IN) and the ground (GND) of the mobile phone respectively. However, the arrangement of these contact points on an audio plug is not standardized yet. The contact point of MIC-IN and GND may be reversed in some mobile phones. Hence, at least two different designs of the accessory devices are required to make them compatible with all mobile phones. This is not desirable for the merchants, because it increases the number of Stock Keeping Units (SKU) of an accessory device. This is also not desirable for the consumers, because it makes it difficult to identify and choose a suitable accessory device for their mobile phones.
Accordingly, there is a need for a method of identifying the specific GND and MIC-IN configuration in the audio plug of a mobile phone.